Method for improving flame retardant efficiency of phenoxyphosphazene compound, and prepreg. laminate for printed circuit made by the method

ABSTRACT

The present invention provides a method for improving the flame retardant efficiency of a phenoxyphosphazene compound, and provides a prepreg, a laminate, and a laminate for printed circuit that are made by the method. The present invention compounds a phenoxyphosphazene compound and a dihydrobenzoxazine ring-containing compound in a halogen-free flame retardant resin composition, so as to effectively improve the flame-retardant efficiency of the phenoxyphosphazene compound. Besides, the prepreg, the laminate and the laminate for printed circuit that are made by the method for improving the flame retardant efficiency of a phenoxyphosphazene compound have excellent flame retardancy, chemical resistance, anti-CAF property, high glass transition temperature (Tg), high thermal resistance, low dielectric dissipation factor, low moisture, and low C.T.E, etc. Furthermore, epoxy resins are interfused to greatly overcome the brittleness of the benzoxazine resin, so, the cured resin has comparatively high flexural strength and good processability.

FIELD OF THE INVENTION

The present invention relates to a method for improving the flameretardant efficiency of a phenoxyphosphazene compound, and relates to aprepreg, a laminate, and a laminate for printed circuit that are made bythe method.

BACKGROUND OF THE INVENTION

Since always, laminates used for printed circuit usually adopt a halogenflame retardant to prevent burning, and particularly adopttetrabromobisphenol-A epoxy resin. This brominated epoxy resin has goodflame retardancy, but it will produce poisonous hydrogen bromide gaswhen buring. Besides, in recent years, carcinogens, such as dioxin anddibenzofuran, are detected in the combustion products of wasteelectrical and electronic equipments containing halogens such aschlorine and bromine. So, the application of brominated epoxy resins islimited.

With the EU directives on WEEE (Waste Electrical and ElectronicEquipment) and RoHS (Restriction of Hazardous Substances in Electricaland Electronic Equipment) being put into practice on Jul. 1, 2006,developing halogen-free and flame-retardant laminates used in printedcircuits has become the key work of the industry.

On the other hand, with the lead-free times coming, for a printedcircuit board, besides the halogen-free flame retardant property, thefunction of being compatible with lead-free soldering also becomesimportant. So, laminates used for printed circuit also require morethermal resistance and reliability than ever before.

To solve the above mentioned problems, the Chinese patent No.ZL200410051855.3 disclosed a resin composition that adoptsphosphorus-containing epoxy resin and bisphenol-A benzoxazine resin asthe base resin. The cured resin has high glass transition temperature(Tg), high thermal resistance, low dielectric dissipation factor, lowC.T.E, and good flame retardancy. But, because the base resin isphosphorus-containing epoxy resin and bisphenol-A benzoxazine resin, thecured resin is comparatively brittle, and has general processability,low flexural strength and comparatively poor chemical resistance.

And, the Chinese patent No. ZL02803484.8 disclosed a resin compositionthat adopts bisphenol-F benzoxazine resin and bisphenol-F epoxy resin asthe base resin. The cured resin has high glass transition temperature(Tg), high thermal resistance, high modulus of elasticity, lowdielectric dissipation factor, good flame retardancy, and goodprocessability. But, because a condensed phosphate type flame retardantis added to the resin composition, the chemical resistance and anti-CAFproperty of the cured resin can not be guaranteed, that is, the longterm reliability is under great risk.

Besides, the Chinese patent No. ZL01814589.2 disclosed an epoxy resincomposition of halogen-free flame retardant type that adopts aphenoxyphosphazene compound. The laminates used for printed circuit thatuse the resin composition have good thermal resistance, low moisture andgood flame retardancy. But, comparing the above mentionedphenoxyphosphazene flame retardant with common phosphorus-containingflame retardants (such as condensed phosphate), it can be dissolved inan organic solvent, and be easily evenly distributed in a resincomposition. And, it has the advantages such as having a comparativelyhigh thermal decomposition temperature, having low moisture, and beinghard to hydrolyze. But, because the base resin of the resin compositionin the patent is an ordinary epoxy resin and phenolic resin, which doesnot have flame retardancy itself, plenty of phenoxyphosphazene compound(about 23-31 wt %) must be added to it in order to impart enough flameretardancy, and the flame-retardant efficiency is not high. If thelaminates are at high temperature condition, the phenoxyphosphazenecompound may migrate or even bleed out, and the physical properties suchas flexural strength will fall off sharply.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a method for improvingthe flame retardant efficiency of a phenoxyphosphazene compound, whichcompounds a phenoxyphosphazene compound and a dihydrobenzoxazinering-containing compound in a halogen-free flame retardant resincomposition. The dihydrobenzoxazine ring-containing compound cansynergetically accelerate and initiate the phenoxyphosphazene compoundreleasing flame retardant materials, so the flame retardant efficiencyof the phenoxyphosphazene compound can be greatly increased.

Another object of the present invention is to provide a prepreg, alaminate and a laminate for printed circuit that are made by the methodfor improving the flame retardant efficiency of a phenoxyphosphazenecompound, which have excellent flame retardancy, as well as have highglass transition temperature (Tg), high thermal resistance, highflexural strength, high reliability, low dielectric dissipation factor,low moisture, low C.T.E, good chemical resistance, and goodprocessability.

To achieve the above mentioned objects, the present invention provides amethod for improving the flame retardant efficiency of aphenoxyphosphazene compound, which comprises the following steps:compounding a dihydrobenzoxazine ring-containing compound and thephenoxyphosphazene compound in a halogen-free flame retardant resincomposition, wherein, the weight ratio between the phenoxyphosphazenecompound and the dihydrobenzoxazine ring-containing compound is between1:10 and 1:2.

The softening point of the phenoxyphosphazene compound is between 60° C.and 150° C. The phenoxyphosphazene compound is a mixture of thecyclophenoxyphosphazene compounds shown with the structural formula (α)and the linear phenoxyphosphazene compounds shown with the structuralformula (β), and the components of the phenoxyphosphazene compound areas the following: hexaphenoxycyclotriphosphazene compound (m=3), ofwhich the weight ratio is between 70% and 90%;octaphenoxycyclotetraphosphazene compound (m=4), of which the weightratio is between 3% and 20%; other cyclophenoxyphosphazene compounds(m≧5) and the linear phenoxyphosphazene compounds, of which the weightratio are between 1% and 10%;

wherein, m represents an integer between 3 and 25;

wherein, X represents —N═P(OC₆H₅)₃ or —N═P(O)C₆H₅, and Y represents—P(OC₆H₅)₄ or —P(O)(C₆H₅)₂; n represents an integer between 3 and 100.

The dihydrobenzoxazine ring-containing compound comprises at least oneof the bisphenol-A benzoxazine resin, bisphenol-F benzoxazine resin,phenolphthalein benzoxazine resin, and MDA (4,4′-Methylenedianiline)benzoxazine resin shown with the structural formula (γ) or (δ)relatively;

Wherein, R is

and R1 is

The halogen-free flame retardant resin composition also comprises apolyepoxy compound, a phenolic resin type hardener, and an imidazoletype curing accelerator.

Calculating according to the parts by weight of organic solids, thehalogen-free flame retardant resin composition comprises the followingcomponents:

40-80 parts by weight of the mixture of the phenoxyphosphazene compoundand the dihydrobenzoxazine ring-containing compound, and, the weightratio between the phenoxyphosphazene compound and the dihydrobenzoxazinering-containing compound is between 1:10 and 1:2;

15-45 parts by weight of a polyepoxy compound;

5-25 parts by weight of a phenolic resin type hardener;

0.1-1 parts by weight of an imidazole type curing accelerator.

The polyepoxy compound is at least one selected from bisphenol-A epoxyresin, bisphenol-F epoxy resin, phenol novolac epoxy resin, o-cresolnovolac epoxy resin, bisphenol-A novolac epoxy resin, oxazolidonering-containing halogen-free epoxy resin, and epoxide polybutadiene. Thephenolic resin type hardener is at least one selected from phenolnovolac resin, bisphenol-A novolac resin, nitrogen-containing novolacresin, and phosphorus-containing novolac resin. The imidazole typecompound is at least one selected from 2-methylimidazole,2-ethyl-4-methylimidazole, 2-phenylimidazole, and 2-undecylimidazole.

The halogen-free flame retardant resin composition also comprises 6-300parts by weight of an inorganic filler. The inorganic filler is amixture of aluminium hydroxide and/or silica and other inorganicfillers.

The present invention also provides a prepreg made by the method forimproving the flame-retardant efficiency of a phenoxyphosphazenecompound, which comprises a base material and a halogen-free flameretardant resin composition that adheres to the base material after thebase material is impregnated in the resin composition and then is dried.

The present invention also provides a laminate made by the method forimproving the flame-retardant efficiency of a phenoxyphosphazenecompound, which comprises a plurality of prepregs mutually overlapped;each prepreg includes a base material, and a halogen-free flameretardant resin composition that adheres to the base material after thebase material is impregnated in the resin composition and then is dried.

The present invention also provides a laminate used for printed circuitand made by the method for improving the flame-retardant efficiency of aphenoxyphosphazene compound, which comprises a plurality of prepregsmutually overlapped and a metal foil arranged to one or two surfaces ofthe is overlapped prepregs; each prepreg includes a base material, and ahalogen-free flame retardant resin composition that adheres to the basematerial after the base material is impregnated in the resin compositionand then is dried.

The advantages of the present invention are that: the present inventionprovides the method for improving the flame-retardant efficiency of aphenoxyphosphazene compound, which compounds a phenoxyphosphazenecompound and a dihydrobenzoxazine ring-containing compound. Thephenoxyphosphazene compound and the dihydrobenzoxazine ring-containingcompound have a strong synergetic flame retardant effect. So, at thecondition of greatly reducing the usage amount of the phenoxyphosphazenecompound, the flame retardancy can still be achieved. That is, theflame-retardant efficiency is greatly improved. Moreover, when the curedresin of the halogen-free flame retardant resin composition is at hightemperature condition, the problems such as the phenoxyphosphazenecompound migrating or even bleeding out and the physical properties likeflexural strength falling off sharply will not occur. Besides, thehalogen-free flame retardant resin composition adopts aphenoxyphosphazene compound as the flame retardant, and adopts abenzoxazine resin as the base resin. So, the prepreg, the laminate andthe laminate for printed circuit that are made from the halogen-freeflame retardant resin composition have excellent flame retardancy,chemical resistance, anti-CAF property, high glass transitiontemperature (Tg), high thermal resistance, low dielectric dissipationfactor, low moisture, and low C.T.E, etc. Furthermore, epoxy resins areintroduced to greatly overcome the brittleness of the benzoxazine resin,so, the cured resin has comparatively high flexural strength and goodprocessability.

The characteristic and the technical solution of the present inventionare best understood from the following detailed description.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

To further set forth the technical solution adopted by the presentinvention and the effects thereof, the present invention is describeddetailedly with reference to the following preferred embodiments.

A method of the present invention for improving the flame-retardantefficiency of a phenoxyphosphazene compound, compounds thephenoxyphosphazene compound and a dihydrobenzoxazine ring-containingcompound in a halogen-free flame retardant resin composition. Thehalogen-free flame retardant resin composition, calculating according tothe parts by weight of organic solids, comprises:

(A) 40-80 parts by weight of the mixture of a phenoxyphosphazenecompound (A1) and a dihydrobenzoxazine ring-containing compound (A2),the weight ratio between the phenoxyphosphazene compound (A1) and thedihydrobenzoxazine ring-containing compound (A2) is between 1:10 and1:2;

(B) 15-45 parts by weight of a polyepoxy compound;

(C) 5-25 parts by weight of a phenolic resin type hardener;

(D) 0.1-1 parts by weight of an imidazole type compound as the curingaccelerator.

In the present invention, the phosphorus content of the halogen-freeflame retardant resin composition is controlled to be between 1 wt % and5 wt %, and the nitrogen content is controlled to be between 1 wt % and10 wt %, and the halogen content is controlled to be below 0.09 wt %.The following detailed description describes the components of thepresent invention.

In the present invention, the softening point of the phenoxyphosphazenecompound (A1) in the component (A) is between 60° C. and 150° C., whichis a mixture of the cyclophenoxyphosphazene compounds shown with thestructural formula (α) and the linear phenoxyphosphazene compounds shownwith the structural formula (β), and the components of thephenoxyphosphazene compound (A1) are as the following:

{circle around (1)} hexaphenoxycyclotriphosphazene compound (m=3), ofwhich the weight ratio is between 70% and 90%;

{circle around (2)} octaphenoxycyclotetraphosphazene compound (m=4), ofwhich the weight ratio is between 3% and 20%;

{circle around (3)} the linear phenoxyphosphazene compounds, of whichthe weight ratio are between 1% and 10%;

wherein, m represents an integer between 3 and 25;

wherein, X represents —N═P(OC₆H₅)₃ or —N═P(O)C₆H₅, and Y represents—P(OC₆H₅)₄ or —P(O)(C₆H₅)₂; n represents an integer between 3 and 100.

Comparing to common condensed phosphate flame retardants, thephenoxyphosphazene compound (A1) can be dissolved in an organic solvent,and is easily evenly distributed in a resin composition. And, it hasadvantages of having a comparatively high thermal decompositiontemperature, having low moisture, and being hard to hydrolyze. If thecomponents of the phenoxyphosphazene compound (A1) are all thecyclophenoxyphosphazene compound, its dissolubility in an organicsolvent will be not good. So, a certain amount of linearphenoxyphosphazene compound must be contained to prompt itsdissolubility. But the content of the linear phenoxyphosphazene compoundmust be moderate, or will lead to the softening point of thephenoxyphosphazene compound (A1) being relatively low. Besides, if thesoftening point of the phenoxyphosphazene compound (A1) is lower than60° C., the glass transition temperature of the cured resin will bereduced. If the softening point is higher than 150° C., thecompatibility between the phenoxyphosphazene compound and the othercomponents will become bad. If the usage amount of thephenoxyphosphazene compound (A1) is too little, the flame retardanteffect can not be obtained. If the usage amount is too much, the otherproperties of the cured resin will be affected. If the cured resin is athigh temperature condition, the phenoxyphosphazene compound (A1) maymigrate or even bleed out, and the physical properties such as flexuralstrength will fall off sharply.

In the present invention, the phenoxyphosphazene compound (A1) is anitrogen-containing or phosphorus-containing flame retardant. Itsflame-retardant mechanism comprises gas phase flame retardation andsolid phase flame retardation. But if it is used alone, the flameretardant material is released comparatively slowly, that is, theflame-retardant efficiency is not high. By compounding thedihydrobenzoxazine ring-containing compound (A2) that has flameretardancy itself and the phenoxyphosphazene compound (A1), they cansynergetically accelerate and initiate the phenoxyphosphazene compound(A1) releasing flame retardant materials, so the flame-retardantefficiency can be greatly increased.

In the present invention, the dihydrobenzoxazine ring-containingcompound (A2) in the component (A) can be prepared with ahydroxyl-containing phenols compound, primary amine and formaldehyde viathe following reaction, and it comprises at least one of bisphenol-Abenzoxazine resin, bisphenol-F benzoxazine resin, phenolphthaleinbenzoxazine resin, and MDA (4,4′-Methylenedianiline) benzoxazine resinshown with the structural formula (γ) or (δ) relatively.

Wherein, R is

and R1 is

For methylene exists in the molecular structure of the above mentionedbisphenol-F benzoxazine resin, the backbone has a comparatively goodtoughness while keeping a certain rigidity, and phenolphthaleinbenzoxazine resin and MDA benzoxazine resin have better heat resistance.The said benzoxazine resins can be used alone or along with each other.

The usage amount of the component A had better be 40-80 parts by weight,and, to guarantee the good synergetic flame retardant effect between thephenoxyphosphazene compound (A1) and the dihydrobenzoxazinering-containing compound (A2), and to avoid the negative effects of thephenoxyphosphazene compound (A1), the weight ratio between thephenoxyphosphazene compound (A1) and the dihydrobenzoxazinering-containing compound (A2) is preferred to be between 1:10 and 1:2.

The component (B) of the present invention, that is, the polyepoxycompound, particularly includes bisphenol-A epoxy resin, bisphenol-Fepoxy resin, phenol novolac epoxy resin, o-cresol novolac epoxy resin,bisphenol-A novolac epoxy resin, oxazolidone ring-containinghalogen-free epoxy resin, and epoxide polybutadiene. According to thepurpose, they can be used by oneself, or can be used after being mixed.For example, a cured resin that uses bisphenol-F epoxy resin has goodtoughness, and, a cured resin that uses bisphenol-A novolac epoxy resinor o-cresol novolac epoxy resin has a comparatively high glasstransition temperature. The usage amount of the polyepoxy compound is15-45 parts by weight, and preferably is 20-40 parts by weight.

The component (C) of the present invention, that is, the phenolic resintype hardener, particularly includes phenol novolac resin, bisphenol-Anovolac resin, nitrogen-containing novolac resin, andphosphorus-containing novolac resin. They can be used alone, or can beused with each other. Nitrogen-containing novolac resin orphosphorus-containing novolac resin is preferred, since they has goodflame retardancy, and can increase the glass transition temperature (Tg)of a cured resin. Its usage amount is preferred to be 5-25 parts byweight if it is lower than 5 parts by weight, the glass transitiontemperature of the cured resin is increased not much, and if it ishigher than 25 parts by weight, the thermal resistance of the curedresin will become bad.

The component (D) of the present invention, that is, the imidazole typecuring accelerator, may be at least one compound of 2-methylimidazole,2-ethyl-4-methylimidazole, 2-phenylimidazole, and 2-undecylimidazole.

The present invention can also comprises a component (E), that is, theinorganic filler. The inorganic filler is used to adjust some physicalproperties of the composition. The inorganic filler may be a generalinorganic filler such as aluminium hydroxide, magnesium hydroxide,zeolite, wollastonite, silica, magnesium oxide, calcium silicate,calcium carbonate, day, talcum powder and mica. The inorganic filler canbe selected according to the use. Particularly, aluminium hydroxide andsilica are preferred, since they can be used as the flame retardantadditive for the phenoxyphosphazene compound. If the organic solids inthe halogen-free flame retardant epoxy composition are 100 parts byweight, the usage amount of the inorganic filler is 6-300 parts byweight, and preferably 30-100 parts by weight.

The present invention also provides a prepreg made by the method forimproving the flame-retardant efficiency of a phenoxyphosphazenecompound, which comprises a base material, and a halogen-free flameretardant resin composition that adheres to the base material after thebase material is impregnated in the resin composition and then is dried.

The present invention also provides a laminate made by the method forimproving the flame-retardant efficiency of a phenoxyphosphazenecompound, which comprises a plurality of prepregs mutually overlapped;each prepreg includes a base material, and a halogen-free flameretardant resin composition that adheres to the base material after thebase material is impregnated in the resin composition and then is dried.

The present invention also provides a laminate for printed circuit madeby the method for improving the flame-retardant efficiency of aphenoxyphosphazene compound, which comprises a plurality of prepregsmutually overlapped and a metal foil arranged to one or two surfaces ofthe overlapped prepregs; each prepreg includes a base material, and ahalogen-free flame retardant resin composition that adheres to the basematerial after the base material is impregnated in the resin compositionand then is dried.

The prepreg of the present invention is made by heating and drying theabove mentioned halogen-free flame retardant resin composition, whichuses a nonwoven fabric or other fabrics, such as natural fiber, organicsynthesis fiber, and inorganic fiber, as the base material. The regularpreparation method of the resin composition of the present inventioncomprises: first adding solids in, and then adding a liquid solvent in;stirring until the solids are completely dissolved, then adding a liquidresin and an accelerator in, and then continuing to stir evenly; finallyadding PM (1-Methoxy-2-propanol) solvent in to adjust the solid contentof the solution to be in the range of 65%-75%, so as to obtain a liquidvarnish, that is, the halogen-free flame retardant resin of the presentinvention; dipping a fabric or an organic fabric, such as a glass cloth,in the liquid varnish; heating and drying the impregnated glass cloth inan oven at 160° C. for 4 minutes, thereby obtaining the resincomposition of the present invention.

The laminate for printed circuit of the present invention comprises alaminate that is made by two or over two pieces of prepregs being bondedtogether via heating and pressurizing, and a metal foil that is bondedto one or two surfaces of the laminate. The laminate is made from eightpieces of the above mentioned prepregs and two pieces of one ounce metalfoils (35 μm thick), which are mutually overlapped and then laminated ina laminating machine, so as to produce a laminate with double metal foilsurfaces. The lamination should meet the following requirements that:{circle around (1)} the lamination heating rate generally should becontrolled in the range of 1.5-2.5° C./min while the materialtemperature is in the range of 80° C.-140° C.; {circle around (2)} whilethe outer layer material temperature is in the range of 80° C.-100° C.,a full lamination pressure of about 350 psi should be applied; {circlearound (3)} while curing, the material temperature is controlled at 185°C. and kept for 60 min. The material of the metal foil is not limited,which can be a copper foil, a nickel foil, an aluminum foil, or a SUSfoil, etc.

By measuring properties, such as dielectric dissipation factor, thermalresistance, moisture, C.T.E, glass transition temperature, and flameretardancy, of the above mentioned produced laminate (eight pieces ofprepregs) used for printed circuit, the present invention is furtherdetailedly described with the following embodiments.

Please refer to the embodiments 1-12, and the comparison examples 1-6.

The embodiments of the present invention are detailedly described asfollows. The embodiments are not to limit the scope of the presentinvention. Hereinafter, unless special explanation, the part representsparts by weight, and “%” represents weight percent.

(A1) phenoxyphosphazene compound

SPB-100 (trade name of Otsuka Chemical Co., Ltd);

(A2) dihydrobenzoxazine ring-containing compound

(A2-1) LZ 8280 (trade name of Huntsman Advanced Materials);

(A2-2) D125(trade name of Sichuan EM Technology;

(B) halogen-free epoxy resin

(B-1) XZ 97103 (trade name of Dow Chemical)

(B-2) EPON SU-8 (trade name of Hexion Specialty Chemicals);

(C) phenolic resin type hardener

(C-1) PHL6635 (trade name of Hexion Specialty Chemicals)

(C-2) PS 6313 (trade name of GUN EI CHEMICAL INDUSTRY CO., LTD.)

(C-3) XZ 92741 (trade name of Dow Chemical)

(D) curing accelerator

2-phenylimidazole (SHIKOKU Chemicals Co.)

(E) inorganic filler

(E-1) aluminium hydroxide (purity over 99%)

(E-2) silica (purity over 99%)

TABLE 1 Formula of Composition I (parts by weight) Embodiment 1Embodiment 2 Embodiment 3 Embodiment 4 Embodiment 5 Embodiment 6 A1 1818 18 18 18 18 A2-1 45 45 45 45 A2-2 45 45 B-1 25 25 25 B-2 25 25 25 C-14 7 7 4 7 4 C-2 7 4 4 7 4 7 D 1.0 1.0 1.0 1.0 1.0 1.0 E-1 E-2

TABLE 2 Formula of Composition II (parts by weight) Embodiment 7Embodiment 8 Embodiment 9 Embodiment 10 Embodiment 11 Embodiment 12 A118 15 15 15 15 15 A2-1 25 46 46 26 A2-2 20 46 46 20 B-1 26 26 B-2 25 2626 26 C-1 4 8 4 8 4 4 C-2 7 4 8 4 8 8 D 1.0 1.0 1.0 1.0 1.0 1.0 E-1 3010 30 10 10 E-2 10 30 10 30 30

TABLE 3 Formula of Composition III (parts by weight) ComparisonComparison Comparison Comparison Comparison Comparison example 1 example2 example 3 example 4 example 5 example 6 A1 15 15 15 10 25 25 A2-1 4646 46 53 35 A2-2 35 B-1 26 16 24 28 B-2 26 10 28 C-1 4 8 4 8 4 4 C-2 8 47 7 C-3 8 4 D 1.0 1.0 1.0 1.0 1.0 1.0 E-1 20 20 20 20 20 20 E-2 20 20 2020 20 20

TABLE 4 Property evaluation I Embodiment 1 Embodiment 2 Embodiment 3Embodiment 4 Embodiment 5 Embodiment 6 glass 144 156 173 184 167 196transition temperature (Tg, ° C.) peel strength 1.45 1.57 1.43 1.52 1.421.51 (N/mm) flame V-0 V-0 V-0 V-0 V-0 V-0 retardancy (1.60 mm) flame V-0V-0 V-0 V-0 V-0 V-0 retardancy (0.80 mm) solder dipping ◯ ◯ ◯ ◯ ◯ ◯(delamination) solder dipping ◯ ◯ ◯ ◯ ◯ ◯ (measling) moisture 0.11 0.120.10 0.11 0.09 0.09 (%) dielectric 0.005 0.005 0.005 0.005 0.005 0.005dissipation factor (1 GHZ) flexural 630 650 640 640 540 570 strength(N/mm2) punchability ◯ ◯ ◯ ◯ ◯ ◯ halogen 0.03 0.03 0.03 0.03 0.03 0.03content (%) migration ◯ ◯ ◯ ◯ ◯ ◯ resistanceanti-CAF >1000 >1000 >1000 >1000 >1000 >1000 property (hr) alkali ◯ ◯ ΔΔ ◯ Δ resistance

TABLE 5 Property evaluation II Embodiment 7 Embodiment 8 Embodiment 9Embodiment 10 Embodiment 11 Embodiment 12 glass 192 151 163 175 201 198transition temperature (Tg, ° C.) peel strength 1.44 1.42 1.51 1.40 1.481.43 (N/mm) flame V-0 V-0 V-0 V-0 V-0 V-0 retardancy (1.60 mm) flame V-0V-0 V-0 V-0 V-0 V-0 retardancy (0.80 mm) solder dipping ◯ ◯ ◯ ◯ ◯ ◯(delamination) solder dipping ◯ ◯ ◯ ◯ ◯ ◯ (measling) moisture 0.10 0.080.08 0.08 0.08 0.08 (%) dielectric 0.005 0.005 0.005 0.005 0.005 0.005dissipation factor (1 GHZ) flexural 550 550 550 550 550 550 strength(N/mm2) punchability ◯ ◯ ◯ ◯ ◯ ◯ halogen 0.03 0.03 0.03 0.03 0.03 0.03content (%) migration ◯ ◯ ◯ ◯ ◯ ◯ resistanceanti-CAF >1000 >1000 >1000 >1000 >1000 >1000 property (hr) alkali Δ ◯ Δ◯ Δ Δ resistance

TABLE 6 Property evaluation III Comparison Comparison ComparisonComparison Comparison Comparison example 1 example 2 example 3 example 4example 5 example 6 glass transition 149 157 159 210 141 153 temperature(Tg, ° C.) peel strength 1.39 1.41 1.51 1.40 1.48 1.43 (N/mm) flameretardancy V-0 V-0 V-0 V-0 V-0 V-0 (1.60 mm) flame retardancy V-0 V-1V-0 V-0 V-0 V-0 (0.08 mm) solder dipping ◯ ◯ ◯ ◯ ◯ ◯ (delamination)solder dipping ◯ ◯ ◯ ◯ ◯ ◯ (measling) moisture 0.12 0.13 0.09 0.09 0.090.09 (%) dielectric 0.005 0.005 0.005 0.005 0.005 0.005 dissipationfactor (1 GHZ) flexural strength 530 510 540 490 500 500 (N/mm2)punchability ◯ ◯ ◯ ◯ ◯ ◯ halogen content 0.03 0.03 0.03 0.03 0.03 0.03(%) migration ◯ ◯ ◯ ◯ Δ Δ resistance anti-CAFproperty >1000 >1000 >1000 >1000 >1000 >1000 (hr) alkali resistance ◯ Δ◯ ◯ Δ ◯

Test method of the above mentioned properties is as follows.

(a) Glass Transition Temperature

According to differential scanning calorimetry, glass transitiontemperature is measured by the DSC method stated in IPC-TM-650 2.4.25.

(b) Peel Strength

According to the experiment condition of “After Thermal Stress” in themethod stated in IPC-TM-650 2.4.8, the peel strength of metal coverlayer is measured.

(c) Flame-retardant Property

Flame-retardant property is measured according to the standard of UL94.

(d) Solder Dipping

The sample (a base material of 100×100 mm) is kept for 2 hours in apressure cooking processing device at 121° C. at 105 Kpa, then it isimpregnated in a solder bath at 260° C. for 20 seconds; by visualinspection, it is viewed whether delaminating exists or not, and it isalso viewed whether crazing exists or not. In the tables, symbol ◯represents that nothing changes; symbol Δ represents that measlingoccurs; symbol x represents that delamination occurs.

(e) Moisture

Moisture is measured according to the method stated in IPC-TM-6502.6.2.1.

(f) Dielectric Dissipation Factor

By the resonance method using a strip line, dielectric dissipationfactor at 1 GHz are measured according to IPC-TM-650 2.5.5.5.

(g) Flexural Strength

According to the method stated in IPC-TM-650 2.4.4, at room temperature,loads are applied to the sample of specific dimension and shape tomeasure.

(h) Punchability

Punch a base material of 1.6 mm thickness with a punching die device ofa certain figure, and then it is viewed by visual inspection. Whereinthe tables, symbol ◯ represents that no haloing is at the hole edge.Symbol Δ represents that the hole edge is provided with a haloing.Symbol x represents that the hole edge is cracked.

(i) Halogen Content

According to Test Method for Halogen-free Materials stated inJPCA-ES-01-2003, the halogen content of a copper clad laminate ismeasured by oxygen flask combustion method and ion chromatography.

(j) Migration Resistance

Heat a base material of 100×100 mm in an oven at 200° C. for 4 hours,and then it is viewed by visual inspection. Wherein the tables, symbol ◯represents that nothing bleeds out. Symbol Δ represents bleeding out alittle. Symbol X represents bleeding out much.

(k) Anti-CAF Property

It is measured according to the method stated in the company standardQ/DZAD650 2.6.25 of Guangdong Shengyi Sci. Tech Co., Ltd.

(j) Alkali Resistance

Dip a base material of 50×50 mm in 10% sodium hydroxide solution at 80°C. for 60 minutes, and then it is viewed by visual inspection. In thetables, symbol ◯ represents that nothing changes. Symbol Δ representsmeasling. Symbol X represents delamination and blister.

In summary, the present invention compounds a phenoxyphosphazenecompound and a dihydrobenzoxazine ring-containing compound in ahalogen-free flame retardant resin composition. The strong synergeticflame retardant effect between the phenoxyphosphazene compound and thedihydrobenzoxazine ring-containing compound can effectively improve theflame-retardant efficiency of the phenoxyphosphazene compound. So, atthe condition of greatly reducing the usage amount of thephenoxyphosphazene compound, the flame retardancy can still be achieved.Moreover, when the cured resin of the halogen-free flame retardant resincomposition is at high temperature condition, the problems such as thephenoxyphosphazene compound migrating or even bleeding out and thephysical properties like flexural strength falling off sharply will notoccur. Besides, the halogen-free flame retardant resin compositionadopts a phenoxyphosphazene compound as the flame retardant, and adoptsa benzoxazine resin as the base resin, so, the prepreg, the laminate andthe laminate for printed circuit that are made from the halogen-freeflame retardant resin composition have excellent flame retardancy,chemical resistance, anti-CAF property, high glass transitiontemperature (Tg), high thermal resistance, low dielectric dissipationfactor, low moisture, and low C.T.E, etc. Furthermore, epoxy resins areintroduced to greatly overcome the brittleness of the benzoxazine resin,so, the cured resin has comparatively high flexural strength and goodprocessability.

Although the present invention has been described in detail with abovesaid embodiments, but it is not to limit the scope of the invention. So,all the modifications and changes according to the characteristic andspirit of the present invention, are involved in the protected scope ofthe invention.

What is claimed is:
 1. A method for improving the flame retardantefficiency of a phenoxyphosphazene compound, comprising the followingsteps: compounding a dihydrobenzoxazine ring-containing compound and thephenoxyphosphazene compound in a halogen-free flame retardant resincomposition, wherein, the weight ratio between the phenoxyphosphazenecompound and the dihydrobenzoxazine ring-containing compound is between1:10 and 1:2, wherein the softening point of the phenoxyphosphazenecompound is between 60° C. and 150° C.; the phenoxyphosphazene compoundis a mixture of the cyclophenoxyphosphazene compounds shown with thestructural formula (α) and the linear phenoxyphosphazene compounds shownwith the structural formula (β), and the components comprise thefollowing: hexaphenoxycyclotriphosphazene compound, wherein m=3, ofwhich the weight ratio is between 70% and 90%;octaphenoxycyclotetraphosphazene compound, wherein m=4, of which theweight ratio is between 3% and 20%; and other cyclophenoxyphosphazenecompounds, wherein m≧5, and the linear phenoxyphosphazene compounds, ofwhich the weight ratio are between 1% and 10%;

wherein, m represents an integer between 3 and 25;

wherein, X represents —N═P(OC₆H₅)₃ or —N═P(O)C₆H₅, and Y represents—P(OC₆H₅)₄ or —P(O)(C₆H₅)₂; n represents an integer between 3 and 100.2. The method for improving the flame retardant efficiency of aphenoxyphosphazene compound of claim 1, wherein the dihydrobenzoxazinering-containing compound comprises at least one of the bisphenol-Abenzoxazine resin, bisphenol-F benzoxazine resin, phenolphthaleinbenzoxazine resin, and MDA (4,4′-Methylenedianiline) benzoxazine resinshown with the structural formula (γ) or (δ) relatively;

wherein, R is

 and R1 is


3. The method for improving the flame retardant efficiency of aphenoxyphosphazene compound of claim 1, wherein the halogen-free flameretardant resin composition further comprises a polyepoxy compound, aphenolic resin type hardener, and an imidazole type curing accelerator.4. The method for improving the flame retardant efficiency of aphenoxyphosphazene compound of claim 3, wherein, calculating accordingto the parts by weight of organic solids, the halogen-free flameretardant resin composition comprises the following components: 40-80parts by weight of the mixture of the phenoxyphosphazene compound andthe dihydrobenzoxazine ring-containing compound, and, the weight ratiobetween the phenoxyphosphazene compound and the dihydrobenzoxazinering-containing compound being between 1:10 and 1:2; 15-45 parts byweight of a polyepoxy compound; 5-25 parts by weight of a phenolic resintype hardener; 0.1-1 parts by weight of an imidazole type curingaccelerator.
 5. The method for improving the flame retardant efficiencyof a phenoxyphosphazene compound of claim 4, wherein the polyepoxycompound is at least one selected from bisphenol-A epoxy resin,bisphenol-F epoxy resin, phenol novolac epoxy resin, o-cresol novolacepoxy resin, bisphenol-A novolac epoxy resin, oxazolidonering-containing halogen-free epoxy resin, and epoxide polybutadiene; thephenolic resin type hardener is at least one selected from phenolnovolac resin, bisphenol-A novolac resin, nitrogen-containing novolacresin, and phosphorus-containing novolac resin; the imidazole typecompound is at least one selected from 2-methylimidazole,2-ethyl-4-methylimidazole, 2-phenylimidazole, and 2-undecylimidazole. 6.The method for improving the flame retardant efficiency of aphenoxyphosphazene compound of claim 4, wherein the halogen-free flameretardant resin composition further comprises 6-300 parts by weight ofan inorganic filler; the inorganic filler is one of (a) a mixture ofaluminium hydroxide with other inorganic fillers, (b) a mixture ofsilica with other inorganic fillers and (c) a mixture of both aluminiumhydroxide and silica with other inorganic fillers.
 7. A prepreg made bythe method for improving the flame-retardant efficiency of aphenoxyphosphazene compound of claim 1, comprising a base material and ahalogen-free flame retardant resin composition, the halogen-free flameretardant resin composition adhering to the base material after the basematerial being impregnated in the resin composition and then beingdried.
 8. A laminate made by the method for improving theflame-retardant efficiency of a phenoxyphosphazene compound of claim 1,comprising a plurality of prepregs mutually overlapped; each prepregincluding a base material and a halogen-free flame retardant resincomposition, the halogen-free flame retardant resin composition adheringto the base material after the base material being impregnated in theresin composition and then being dried.
 9. A laminate for printedcircuit made by the method for improving the flame-retardant efficiencyof a phenoxyphosphazene compound of claim 1, comprising a plurality ofprepregs mutually overlapped and a metal foil arranged to one or twosurfaces of the overlapped prepregs; each prepreg including a basematerial and a halogen-free flame retardant resin composition, thehalogen-free flame retardant resin composition adhering to the basematerial after the base material being impregnated in the resincomposition and then being dried.